Columns in which a light fluid such as a gas are contacted with a heavier fluid (e.g. liquid) are well known in the art. For example, US2013/0204066 describes a unit for establishing contact between a liquid and a gas which may be used for washing natural gas to extract acid compounds or for drying gas by contacting it with a hydroscopic liquid. US 2012/0118399 describes a process column in which a heavier fluid interacts with a lighter fluid; the column may be a distillation column. US2007/0272326 describes a fractionation column and US2002/0041040 describes a counterflow column. A generic term for such columns may be a process engineering column.
FIGS. 1 and 1d are schematic illustrations of two examples of a state of the art gas-liquid contactor column which may be a carbon dioxide absorber, a distillation column or another similar device. The column of FIG. 1 comprises fluid collectors and redistributors which are particularly suited to off-shore locations in which the column may tilt. If the column were located onshore; simpler fluid collectors and redistributors may be used.
Referring to FIG. 1, a first fluid which may be a liquid is input through a first input 10 which is positioned towards the top of the column. For example, in a carbon dioxide absorber column, the liquid is a solvent (e.g. water and one or more amines) which is suitable for absorbing carbon dioxide. The first input 10 is connected to a fluid distributor 24 an example of which is shown in more detail in FIG. 1a. The fluid distributor 24 is well known in the art and is not described in detail. However, as is clearly shown the fluid distributor comprises a plurality of distribution pipes for evenly distributing the fluid across the cross-section of the column. The fluid then flows downwards through the column through upper packing 22 which is shown in more detail in FIG. 1b. Again, the use of such packing is well known in the art and is not described in detail. The packing may comprise a plurality of layers and may be structured or random. As shown in FIG. 1, two packing beds are used but more packing beds may be used, for example three as shown in FIG. 1d. For example, for carbon-dioxide removal in a floating natural gas (FLNG) or floating production storage and offloading (FPSO) vessel, use of three packing beds is typical.
A second fluid which is lighter than the first fluid and may be a gas is input through a second input 12 which is positioned towards the bottom of the column. For example, in a carbon dioxide absorber column, the second fluid is a gas where carbon dioxide is an impurity which has to be removed. The second fluid rises through the column through another packing bed 22 (lower packing) which may be same as that used below the fluid distributor 24.
The first fluid which has passed through the distributor 24 and the packing 22 falls on to the collector tray of a fluid collector and redistributor 30 which is shown in more detail in FIG. 1c. The redistributor 30 comprises a fluid collection plate 32. The level of fluid on the upper surface of the plate 32 is schematically illustrated by line 20 (in FIG. 1). The second fluid (e.g. gas) which has risen through the column through lower packing 22 passes through chimneys 36 in the collection plate 32. The chimneys 36 pass through the collection plate 32 and are sufficiently tall that the light fluid is output above the level of fluid on the collection plate 32. In this way, there is no contact or interaction between first and second fluids on the collection plate.
The fluid collector and redistributor 30 also comprises at least one (possibly two or more) downcomer pipes 34 through which the heavier fluid passes from the collection plate. The downcomer pipes 34 are connected to a fluid distributor 38. The downcomer pipes 34 may be several meters long and thus there may be a large gap between the collection plate 32 and the fluid redistributor 38. The use of the downcomer pipes to channel the heavier fluid ensures that there is no interaction between the heavier fluid and the gas in the gap between the collection plate or anywhere within the fluid collector and redistributor 30. In this case, the fluid distributor is a branched distributor which comprises a plurality of branches for uniformly distribution of the fluid across the cross-section of the column.
Returning to FIG. 1-1d, the heavier fluid flows down from the distributor 38 through lower packing 22 to collect in a fluid sump 18 at the bottom of the column. The first fluid will interact with the second fluid as it rises through the lower packing 22, e.g. to absorb carbon dioxide. The first fluid, e.g. the solvent which has absorbed the carbon dioxide from the second fluid, is then removed from the column by first fluid output 16 located at the base of the column. Similarly, the first, heavier fluid will interact with the second, lighter fluid as it rises through the upper packing 22, e.g. to absorb carbon dioxide before the first fluid hits the collection plate. Fluid then flows out through a second fluid output 14 located at the top of the column. For example, in a carbon dioxide absorber column, the treated gas is drawn off from the second fluid output. A meshpad 11 may be provided over the second fluid output 14.
Many of these process engineering columns are on a floating production facility, for example a floating natural gas (FLNG) or floating production storage and offloading (FPSO) vessel. One problem is that the columns are affected by tilt and motion of the floating facility. This problem is recognised in the prior art, for example in U.S. Pat. No. 8,118,284, which explains how the heavy fluid may not be uniformly distributed to the packing below the redistributor under tilted and moving conditions. U.S. Pat. No. 8,118,284 describes a pressure distributor which is designed to address this problem. However, the present applicant has recognised the need for further improvement of the redistributor for use in columns which are likely to tilt or move.